1. Field of the Invention
This invention relates generally to implantable electrode assemblies, and more particularly to an electrode assembly comprising a plurality of electrodes organized into a helical structure. The electrodes may be operatively coupled to an implantable medical device (IMD).
2. Description of the Related Art
As used herein, “stimulation” or “stimulation signal” refers to the application of an electrical, mechanical, magnetic, electro-magnetic, photonic, audio and/or chemical signal to a neural structure in the patient's body. The signal is an exogenous signal that is distinct from the endogenous electrical, mechanical, and chemical activity (e.g., afferent and/or efferent electrical action potentials) generated by the patient's body and environment. In other words, the stimulation signal (whether electrical, mechanical, magnetic, electro-magnetic, photonic, audio or chemical in nature) applied to the nerve in the present invention is a signal applied from an artificial source, e.g., a neurostimulator.
A “therapeutic signal” refers to a stimulation signal delivered to a patient's body with the intent of treating a disorder by providing a modulating effect to neural tissue. The effect of a stimulation signal on neuronal activity is termed “modulation”; however, for simplicity, the terms “stimulating” and “modulating”, and variants thereof, are sometimes used interchangeably herein. In general, however, the delivery of an exogenous signal itself refers to “stimulation” of the neural structure, while the effects of that signal, if any, on the electrical activity of the neural structure are properly referred to as “modulation.” The effect of delivery of the stimulation signal to the neural tissue may be excitatory or inhibitory and may potentiate acute and/or long-term changes in neuronal activity. For example, the “modulating” effect of the stimulation signal to the neural tissue may comprise one or more of the following effects: (a) changes in neural tissue to initiate an action potential (afferent and/or efferent action potentials); (b) inhibition of conduction of action potentials (whether endogenous or exogenously induced) or blocking the conduction of action potentials (hyperpolarizing or collision blocking), (c) affecting changes in neurotransmitter/neuromodulator release or uptake, and (d) changes in neuro-plasticity or neurogenesis of brain tissue.
Thus, electrical neurostimulation or modulation of a neural structure refers to the application of an exogenous electrical signal (as opposed to mechanical, chemical, photonic, or another mode of signal delivery) to the neural structure. Electrical neurostimulation may be provided by implanting an electrical device underneath the skin of a patient and delivering an electrical signal to a nerve such as a cranial nerve. In one embodiment, the electrical neurostimulation involves sensing or detecting a body parameter, with the electrical signal being delivered in response to the sensed body parameter. This type of stimulation is generally referred to as “active,” “feedback,” or “triggered” stimulation. In another embodiment, the system may operate without sensing or detecting a body parameter once the patient has been diagnosed with a medical condition that may be treated by neurostimulation. In this case, the system may periodically apply a series of electrical pulses to the nerve (e.g., a cranial nerve such as a vagus nerve) intermittently throughout the day, or over another predetermined time interval. This type of stimulation is generally referred to as “passive,” “non-feedback,” or “prophylactic,” stimulation. The stimulation may be applied by an implantable medical device that is implanted within the patient's body. In another alternative embodiment, the signal may be generated by an external pulse generator outside the patient's body, coupled by an RF or wireless link to an implanted electrode.
Generally, neurostimulation signals that perform neuromodulation are delivered by the implantable device via one or more leads. The leads are generally coupled at a distal end to electrodes, which are coupled to a tissue in the patient's body. Multiple leads/electrodes may be attached to various points of a nerve or other tissue inside a human body for delivery of neurostimulation. Generally, each lead is associated with a separate electrode, particularly when each of the electrodes is intended to perform a different function (e.g., deliver a first electrical signal, deliver a second electrical signal, sense a body parameter, etc.).
Generally, a single electrode is associated with each lead originating from the IMD. The number of leads that originate from the IMD is limited due to the size constraints of the IMD and of the patient's body. Therefore, a limited number of electrodes using state-of-the-art technology can be used to deliver electrical stimulation from an IMD.
Further, state-of-the-art medical systems call for performing a stimulation during a time period that is separate from a time period of performing a sensing function for sensing the patient's biological signals. Further, a first lead associated with a first electrode may deliver a therapeutic electrical signal, while a second lead associated with a second electrode may perform data acquisition for sensing of various biometric parameters in the patient's body. This process may be inefficient since the state-of-the-art generally lacks a system for simultaneously delivering an electrical signal to a neural structure and sensing electrical activity, particularly where associated with the neural structure to which the signal is applied. Further, problems with the state-of-the-art also include a limitation on the number of electrodes that may be employed by an IMD to deliver various stages of therapy and/or sensing functions.